With hydraulically actuated shifting elements the problem arises that if the internal combustion engine is stopped even for only a short time, the clutch supply ducts are drained, which has the disadvantageous result that when the vehicle is restarted, these ducts first have to be filled again. This means that due to the additional time required for filling the clutch supply ducts, spontaneity is affected in a negative manner. In addition, the air present in the cutch supply ducts must be expelled from the ducts and this has a negative effect on the clutch filling times and also on the quality of shifting.
DE 102 305 01 A1 describes a clutch system comprising a clutch device with at least one clutch arrangement having an input side associated with an output shaft of a drive unit and an output side associated with a transmission input shaft, and which can be actuated by means of at least one hydraulic holding cylinder that rotates with it during operation.
The known clutch system comprises a statically arranged control/regulation valve system which is or can be connected on one side to a hydraulic pressure medium source and on the other side, via a rotary passage arrangement, to the hydraulic holding cylinder, such that a pressure medium reservoir is provided which, at least with a useful pressure medium holding area, is arranged above a height level defined by the rotary passage arrangement and from which pressure medium can be supplied to a section of the hydraulic system which comprises the rotary passage arrangement and connects the control/regulation valve arrangement to the hydraulic holding cylinder, in such manner that pressure medium is delivered at least at one leak point on the outflow side in order to counteract an outflow of pressure medium from the hydraulic system section and/or pressure medium is replenished via at least one inflow point into the hydraulic system section in order to compensate for any outflow of pressure medium from the hydraulic system section.
By virtue of this design, the escape of hydraulic medium from the hydraulic system should be reduced, and in particular draining of the clutch supply ducts when the motor stops for a short time should be prevented. Disadvantageously, the design known from DE 102 305 01 A1 is relatively complicated and involves high manufacturing, assembly and maintenance costs.
From DE 196 05 225 A1 a ball valve is known, which is designed such that a valve body, which can be pressed against a valve seat, is arranged to move within a duct and form a seal against a stretch that constitutes the valve seat. In this case the valve body seals so long as it is present in the duct; when the valve body is pushed out of the duct against the pressure of a spring, a gap opens and the valve is then open.